This invention relates to a method of stabilizing metalloaluminophosphate molecular sieves during storage and handling, to stabilized metalloaluminophosphate molecular sieves and metalloaluminophosphate molecular sieve containing catalysts and to their use in adsorption and conversion processes, especially the conversion of oxygenates to olefins.
Olefins are traditionally produced from petroleum feedstock by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s) such as ethylene and/or propylene from a variety of hydrocarbon feedstock. It has been known for some time that oxygenates, especially alcohols, are convertible into light olefin(s). Methanol, the preferred alcohol for light olefin production, is typically synthesized from the catalytic reaction of hydrogen, carbon monoxide and/or carbon dioxide in a methanol reactor in the presence of a heterogeneous catalyst. The preferred methanol conversion process is generally referred to as a methanol-to-olefin(s) process, where methanol is converted to primarily ethylene and/or propylene in the presence of a molecular sieve.
One of the most useful molecular sieves for converting methanol to olefin(s) are the metalloaluminophosphates such as the silicoaluminophosphates (SAPO""s) and the aluminophosphates (ALPO""s). SAPO synthesis is described in U.S. Pat. No. 4,440,871, which is herein fully incorporated by reference. SAPO is generally synthesized by the hydrothermal crystallization of a reaction mixture of silicon-, aluminum- and phosphorus-sources and at least one templating agent. Synthesis of a SAPO molecular sieve, its formulation into a SAPO catalyst, and its use in converting a hydrocarbon feedstock into olefin(s), particularly where the feedstock is methanol, is shown in U.S. Pat. Nos. 4,499,327, 4,677,242, 4,677,243, 4,873,390, 5,095,163, 5,714,662 and 6,166,282, all of which are herein fully incorporated by reference.
It has been discovered that metalloaluminophosphate molecular sieves, especially silicoaluminophosphate (SAPO) molecular sieves, and aluminophosphate (ALPO) molecular sieves are relatively unstable to moisture containing atmospheres such as ambient air when in the calcined or partially calcined state; this state is sometimes referred to as the activated state. It has also been observed that the relative stability is in part related to the nature of the organic templating agent used in the manufacture of the SAPO molecular sieve. Briend et al., J.Phys. Chem. 1995, 99, 8270-8276, teaches that SAPO-34 loses its crystallinity when the template has been removed from the sieve and the detemplated, activated sieve has been exposed to air. Data is presented, however, which suggest that over at least the short term, crystallinity loss is reversible. Even over a period of a couple years, the data suggest that crystallinity loss is reversible when certain templates are used.
U.S. Pat. No. 4,681,864 to Edwards et al. discusses the use of SAPO-37 molecular sieve as a commercial cracking catalyst. It is disclosed that activated SAPO-37 molecular sieve has poor stability. However, stability can be improved by using a particular activation process. According to the process, retained organic template present from the synthesis of the SAPO-37 is removed from the core structure of the sieve just prior to contacting with feed to be cracked. The process calls for subjecting the sieve to a temperature of 400-800xc2x0 C. within the catalytic cracking unit.
U.S. Pat. No. 5,185,310 to Degnan et al. discloses another method of activating silicoaluminophosphate molecular sieve compositions. The method calls for contacting a crystalline silicoaluminophosphate with gel alumina and water, and thereafter heating the mixture to at least 425xc2x0 C. The heating process is first carried out in the presence of an oxygen-depleted gas, and then in the presence of an oxidizing gas. The objective of the heating process is to enhance the acid activity of the catalyst. The acid activity is enhanced as a result of the intimate contact between the alumina and the molecular sieve.
U.S. Pat. No. 6,051,746 to Sun et.al. discloses a process for the conversion of oxygenated organic materials to olefins using a modified small pore molecular sieve catalyst. The molecular sieve catalyst is modified with polynuclear aromatic heterocyclic compounds in which at least three interconnected ring structures are present having at least one nitrogen atom as a ring substituent, and with each ring having at least five ring members.
European Published Application EP-A2-0,203,005 discusses the use of SAPO-37 molecular sieve in a zeolite catalyst composite as a commercial cracking catalyst. According to the document, if organic template is retained in the SAPO-37 molecular sieve until a catalyst composite containing zeolite and the SAPO-37 molecular sieve is activated during use, and if thereafter the catalyst is maintained under conditions wherein exposure to moisture is minimized, the crystalline structure of the SAPO-37 zeolite composite remains stable.
PCT Publication No. WO 00/74848 to Janssen et.al. discloses a method of protecting the catalytic activity of silicoaluminophosphate molecular sieves by covering the catalytic sites with a shield prior to contacting with an oxygenate feedstock. The shielding may be achieved by retaining template within the pores of the molecular sieve, by using carbonaceous materials, or by using an anhydrous gas or liquid environment.
PCT Publication No. WO 00/75072 to Fung et.al. discloses a method for addressing the problems relating to protecting molecular sieves from damage due to contact with moisture and damage due to physical contact. The method requires the heat treatment of a molecular sieve containing a template under conditions effective to remove a portion of the template from the microporous structure and cooling the heated molecular sieve to leave an amount of template or degradation product thereof effective to cover catalytic sites within the microporous structure.
PCT Publication No. WO 00/74846 to Janssen et.al. discloses a method for preserving the catalytic activity of silicoaluminophosphate molecular sieves which comprises the heating of template-containing silicoaluminophosphate in an oxygen depleted environment under conditions effective to provide an integrated catalyst life which is greater than that obtained using a non-oxygen depleted environment.
U.S. Pat. No. 6,051,745 to Wu et.al. is concerned with overcoming the problem of the excessive production of coke, which occurs when some silicoaluminophosphates are used as catalysts in the conversion of oxygenated hydrocarbons to olefins. The solution proposed is the use of nitrided silicoaluminophosphates. Nitridation is achieved by the reaction of the silicoaluminophosphate with ammonia at elevated temperatures, typically in excess of 700xc2x0 C. The nitridation reaction is essentially irreversible and destroys irreversibly the acidic sites of the molecular sieve, as the acidic OH groups are converted to NH2 groups during the nitridation process.
U.S. Pat. No. 4,861,938 to Lewis et.al describes a process for converting feedstocks. Matrix material used in the manufacture of the catalyst for the process may be conditioned prior to catalyst manufacture by exposure to ammonia.
U.S. Pat. No. 5,248,647 to Barger describes a process for the hydrothermal treatment of silicoaluminophosphate molecular sieves. The process requires the treatment to be undertaken at temperatures in excess of 700xc2x0 C. to destroy a large proportion of the acid sites whilst at the same time retaining a significant proportion of the original crystallinity. Also disclosed in this document is a test method for determining the molecular sieve acidity. This test method requires the adsorption of ammonia onto the molecular sieve, followed by desorption within the temperature range of 300 to 600xc2x0 C. and titration of the desorbed ammonia.
As seen from the disclosures described herein, many metalloaluminophosphate molecular sieves will exhibit a shortened catalytic life when exposed to a moisture-containing environment. This loss of catalytic life is, in some instances, irreversible, and can occur over a very short period of time. In essence, this loss of catalytic life is due to a loss in the number of acid catalytic sites. In addition there may be irreversible loss of molecular sieve crystallinity and porosity on ageing during storage and handling after manufacture.
It is desirable therefore to develop methods for the treatment of metalloaluminophosphate molecular sieves and catalysts containing these molecular sieves, which ensure that the catalytic properties and physical properties of these materials, such as porosity and crystallinity, are retained after storage and handling.
The present invention provides a method for the preparation of stabilized metalloaluminophosphate molecular sieves and metalloaluminophosphate molecular sieve containing catalysts, and to their use in conversion processes. The resultant stabilized molecular sieve retains its catalytic activity and its physical properties even after extensive periods of aging in the presence of moisture. It has been found that if metalloaluminophosphate molecular sieves are treated after activation with specific types of compounds then the molecular sieve is stabilized against hydrolytic attack during storage. Importantly the treatment is reversible so that after periods of storage the compounds may be easily removed to re-generate the activated molecular sieve. The process of the present invention utilizes specific nitrogen containing compounds, which may be chemisorbed and/or physisorbed onto the activated molecular sieve. Importantly the nitrogen containing compounds are not irreversibly chemically reacted with the activated molecular sieves so that they may be easily removed. Without being bound by any theory it is believed that the compounds as used in the present invention are chemisorbed and/or physisorbed onto acid sites on the activated molecular sieves. An important sub-class of nitrogen-containing compounds, which may be used and are preferably used in the present invention, are those that have a kinetic diameter greater than the pore size of the activated molecular sieve. Such molecules are unable to enter the pores of the molecular sieve and therefore are excluded from the internal cage of the molecular sieve structure. It has surprisingly been found that although these nitrogen-containing materials are excluded from the cage of the molecular sieves the internal Broensted acid sites of the activated metalloaluminophosphate molecular sieves are protected during storage from hydrolytic attack. In the context of the present invention reference will be made throughout this specification to metalloaluminophosphate molecular sieves; this term as used in this specification encompasses aluminophosphate (ALPO) and silicoaluminophosphate (SAPO) molecular sieves and derivatives of these molecular sieves as hereinbefore and hereinafter described.
In one embodiment, the present invention relates to a method of treating a metalloaluminophosphate molecular sieve, which method comprises
a. treating at least one activated metalloaluminophosphate molecular sieve with one or more nitrogen containing compounds selected from the group consisting of amines, monocyclic heterocyclic compounds, organonitrile compounds and mixtures thereof under conditions to chemisorb and/or physisorb the nitrogen-containing compound with the metalloaluminophosphate molecular sieve.
In another embodiment, the present invention relates to a method for the manufacture of a catalyst composition, which method comprises
a. forming a mixture comprising at least one metalloaluminophosphate molecular sieve treated by the method of claim 1, at least one binder material and/or at least one additional catalytically active material,
b. forming a catalyst composition from the mixture prepared in step a.
In a further embodiment, the present invention relates to a method for treating a catalyst composition, which method comprises
a. forming a catalyst composition comprising at least one activated metalloaluminophosphate molecular sieve with at least one binder material and/or at least one additional catalytically active material,
b. activating the catalyst composition, and
c. treating the catalyst composition with one or more nitrogen containing compounds selected from the group consisting of amines, mono-cyclic heterocyclic compounds, organonitrile compounds and mixtures thereof under conditions to chemisorb and/or physisorb the nitrogen-containing compounds with the activated metalloaluminophosphate molecular sieve.
The present invention also provides a method for protecting a catalyst composition, which method comprises
a. providing a used catalyst composition, and
b. treating the used catalyst composition with one or more nitrogen containing compounds selected from the group consisting of amines, mono-cyclic heterocyclic compounds, organonitrile compounds and mixtures thereof under conditions to chemisorb and/or physisorb the nitrogen-containing compounds with the metalloaluminophosphate molecular sieve.
Preferably in the aforesaid mentioned method for protecting a catalyst composition, the method further comprises calcining the used catalyst composition prior to treatment with the one or more nitrogen containing compound.
As particular embodiments of the methods mentioned above:
the nitrogen-containing compound is a primary, secondary or tertiary amine;
the nitrogen-containing compound is of the following general formula:
NR1R2R3xe2x80x83xe2x80x83(I) 
wherein R1, R2 and R3 may independently one or more of the following groups: C1-C50-alkyl, C3-C50-cycloalkyl, aromatic, alkyl substituted aromatic, such as C1-C50-alkyl substituted aromatic, aromatic substituted aliphatic moieties such as C1-C50-alkylene moieties substituted with one or more aromatic groups, C1-C50-hydroxyalkyl, amino- and/or hydroxyl-substituted C1-C50-alkyl, alkoxyalkyl such as C2-C50-alkoxyalkyl, dialkylaminoalkyl such as C3-C50-dialkylaminoalkyl, alkylaminoalkyl such as C2-C50-alkylaminoalkyl, heterocyclic, aromatic heterocyclic, alkyl substituted heterocyclic and alkyl substituted aromatic heterocyclic, such as C1-C50-alkyl substituted heterocyclic and aromatic heterocyclic compounds, and heterocyclic substituted aliphatic moieties such as C1-C50-alkylene moieties substituted with one or more aromatic groups and R1 and R2 may independently be hydrogen and R1 and R2 may form, with the nitrogen atom, a nitrogen-containing heterocycle, aromatic heterocycle, alkyl substituted heterocycle or alkyl substituted aromatic heterocycle;
the nitrogen-containing compound is chemisorbed and/or physisorbed at a temperature within the range of 0 to 200xc2x0 C.;
the molecular sieve is treated with at least one nitrogen-containing compound in the bulk state;
the nitrogen-containing compound is chemisorbed and/or physisorbed with the molecular sieve for an extended period of at least two hours;
the method further comprises the step of removing the chemisorbed and/or physisorbed nitrogen-containing compounds;
removal of the nitrogen-containing compound is undertaken during manufacture of a catalyst composition;
removal of the nitrogen-containing compound is achieved by introduction of treated molecular sieve in a catalytic conversion process;
the catalytic conversion process is a methanol-to-olefins process;
the molecular sieve is selected from the group consisting of SAPO-11, SAPO-18, SAPO-34, SAPO-35, SAPO-37, SAPO 44, SAPO-47, MCM-2, intergrowth forms of SAPO-34 and SAPO-18, metal containing forms of each of the foregoing, and mixtures thereof;
the molecular sieve has been exposed to an oxygenate prior to the chemisorption and/or physisorption of one or more nitrogen containing compounds selected from the group consisting of amines, mono-cyclic heterocyclic compounds, organonitrile compounds and mixtures thereof.
In a further embodiment, the present invention provides a stabilized metalloaluminophosphate molecular sieve, which comprises at least one activated metalloaluminophosphate molecular sieve and at least one chemisorbed and/or physisorbed nitrogen containing compound selected from the group consisting of amines, monocyclic heterocyclic compounds, organonitrile compounds and mixtures thereof.
In yet another embodiment, the present invention provides the use of one or more nitrogen containing compounds selected from the group consisting of amines, mono-cyclic heterocyclic compounds, organonitrile compounds and mixtures thereof to stabilize an activated molecular sieve during storage and/or handling.
The invention also provides 1 method for storing molecular sieves which method comprises maintaining the molecular sieve in contact with one or more nitrogen containing compounds selected from the group consisting of amines, mono-cyclic heterocyclic compounds, organonitrile compounds and mixtures thereof in a chemisorbed and/or physisorbed state during storage.
The invention further provides a catalyst composition comprising at least one activated metalloaluminophosphate molecular sieve in admixture with at least one binder and/or at least one additional catalytically active material and at least one chemisorbed and/or physisorbed nitrogen containing compounds selected from the group consisting of amines, mono-cyclic heterocyclic compounds, organonitrile compounds and mixtures thereof.
The invention also provides a catalyst composition comprising at least one metalloaluminophosphate molecular sieve having chemisorbed and/or physisorbed thereon one or more nitrogen containing compounds selected from the group consisting of amines, mono-cyclic heterocyclic compounds, organonitrile compounds and mixtures thereof, in admixture with at least one binder and/or at least one additional catalytically active material.
The metalloaluminophosphate molecular sieves and catalyst compositions comprising these molecular sieves as made by or described in the above embodiments and in the detailed description of the present invention find utility in absorption processes and in hydrocarbon conversion processes.
Accordingly, the present invention also provides a process for the conversion of a feedstock into at least one conversion product comprising the steps of:
a. providing a catalyst composition according to or prepared according to the above embodiments and in the detailed description of the invention;
b. removing the chemisorbed and/or physisorbed nitrogen-containing compound to provide an active catalyst composition;
c. contacting the feedstock with the active catalyst composition;
d. recovering at least one conversion product.
In this embodiment, the invention provides processes for the conversion of one or more oxygenates into one or more olefins, of one or more oxygenates and ammonia to alkylamines, of one or more oxygenates and one or more aromatic compound into one or more alkylated aromatic compounds, as well as process for cracking or dewaxing hydrocarbon feedstocks that take place in the presence of one or several metalloaluminophosphate molecular sieves or catalysts according to the present invention.